Fabrication of Silicon Surface Microstructures via Vortex Femtosecond Laser Irradiation for Reusable Substrates in SERS Applications

Surface-enhanced Raman spectroscopy (SERS) is a key technique in analytical chemistry because of its exceptional sensitivity and specificity for detecting a broad spectrum of substances. Herein, a silicon (Si) substrate fabricated using vortex femtosecond laser beams in ambient air is proposed as an innovative, highly sensitive, and reusable platform for advanced SERS applications. The substrate has composite nanostructures adorned with bush-like formations on top of the elongated structures, which is a direct consequence of the orbital angular momentum of the vortex beam. Simulations conducted using COMSOL provide valuable insights into the distribution of hot spots and electromagnetic field across the substrate surface after gold nanoparticles deposition, underscoring the superior SERS detection capabilities of the fabricated substrate using vortex beams as compared to those processed by Gaussian beams. The vortex-fabricated substrate possesses remarkable reusability, stability, and time-resistance. It exhibited outstanding detection performance for malachite green and microcystin-LR, achieving limits of detection values of 3.91 pM and 2.69 pg·mL^-1, respectively. Therefore, the Si substrates fabricated using a vortex femtosecond laser beam is an ideal candidate for advancing SERS sensors to new heights.